Resilient piston stop construction

ABSTRACT

Resilient structure for stopping a high energy piston in short distance at the end of its stroke without generating excessive heat and without exceeding the elasticity of the components. The structure includes two identical resilient members, one disposed in the end of the cylinder and the other carried on the underside of the piston. The member carried by the piston may be used to resiliently, detachably secure a working member to the piston.

United States Patent Rothfuss Sept. 25, 1973 [54] RESILIENT PISTON STOPTI N 3,320,860 5/1967 Bade 92/85 x 3,600 10 68 B 92 85 x 75 Inventor:Robert G. Rothiuss, Cincinnati, Ohio 19 ade ASSigneeI Senco ts, atPrimary ExaminerMartin P. Schwadron Ohio Assistant ExaminerAbeHershkovitz M 1 Attorney-John Melville et a].

21 1 Appl. No.: 230,569

[57] ABSTRACT Resilient structure for stopping a high energy piston in V5" d z gg short distance at theend of its stroke without generat- [58]"55 88 209 ing excessive heat and without exceeding the elasticity 0care of the components. The structure includes two identical resilientmembers, one disposed in the end of the [56] References Clted cylinderand the other carried on the underside of the UNITED STATES PATENTSpiston. The member carried by the piston may be used 2,983,922 5/1961Juilfs 92/85 X to resiliently, detachably secure a working member to 3,160,075 12/1964 Powers 92/85 x the piston 3,205,787 9/1965 Volkmann92/85 X 3,231,255 H1966 Olson 92/85 UX 8 Claims, 2 Drawing Figures i i Lr fi T w l 5 Ma Q RESILIENT PISTON STOP CONSTRUCTION BACKGROUND OF THEINVENTION This invention relates generally to a resilient piston stopand especially to a resilient structure for stopping a high energypiston in a very short distance. The invention has great and particularutility in connection with fluid actuated fastener driving devices, andaccordingly the invention will be described in terms of such anembodiment Generally considered, fluid actuated fastener driving devicesof the type under consideration all include a working cylinder having apiston slidably disposed therein. Upon the admission of suitable fluidpower in the cylinder,.such as for example air under pressure, thepiston is driven rapidly downwardly in a working stroke. A fastenerdriver carried by the piston is effective during the working stroke todrive a fastener fully into a workpiece.

Early fastener driving devices such as shown for example in U.S. Pat.No. 2,585,939 in the name of A. G. Juilfs, issued on Feb. 19, 1952,disclose the use of a spring for returning the piston to its originalposition upon completion of the working stroke. That is, the space inthe working cylinder above the piston was vented to atmosphere, and aconventional spring was effective to move the piston upwardly in areturn stroke. With tools of this type, the provision of a suitablepiston stop did not present a significant problem. In the first place,the early tools were relatively small and hence the piston did notdevelop great energy. Secondly, the entire working stroke of the pistonwas against the force of the spring, and this too tended to retard thevelocity of the piston. v

U.S."Pat. No. 2,983,922 in the name of A. G. Juilfs, issued on May 16,1961, taught the use of a plenum type return system. In other words, atthe conclusion of the working stroke of the piston, a portion of the airunder pressure from the working cylinder was admitted into a returnreservoir, and this air under pressure was utilized to return the pistonin its upward stroke. In a sense, the elimination of the spring returnsystem began to create the necessity for a suitable resilient pistonstop in connection with a pneumatic fastener driving device.

It will further be appreciated by the skilled worker in the art thatfluid actuated fastener driving devices today have become larger andmore powerful. Numerous commercial tools are available which willsatisfactorily drive. three inch staples, or d common nails into hardwood.

Under these circumstances, the problem of the provision of a suitablepiston stop are greatly magnified. The power of these fastener drivingdevices is such that the driving resistance of the fastener uponpenetration of the workpiece has relatively little effect in stoppingthe fastener. The final or fully driven position of the fastener isdetermined almost entirely by the relative position between the end ofthe fastener driver and the nose piece of the tool when the piston is atthe bottom position. The piston stop assembly of course determines inpart this relative position of the components.

In other words, in a fluid actuated fastener driving tool, the pistonstop construction. must bring a very high energy piston to a full stopin the space of approxiprior art constructions are subject to extremewear and rapid deterioration (if not total destruction) when utilizedwith high energy, more efficient fluid actuated tools.

Keeping the foregoing comments in mind, it is a primary object of thisinvention to provide a resilient structure for stopping a very highenergy piston in a short distance at the end of its stroke.

It is a more specific object of the invention to provide such astructure which will stop a piston without generating excess heat andwithout exceeding the elasticity of the components. This of courseresults in greatly increased life and durability of the piston stopcomponents.

SUMMARY OF THE INVENTION The resilient piston stop structure of thisinvention contemplates the provision of two identical resilient members.One of these resilient members is disposed in the bottom end of aworking cylinder, and the other is carried on the underside of theworking piston.

In a specific embodiment of the invention, the resilient componentcarried by the underside of the piston may be utilized to resiliently,detachably secure a working member to the piston.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view ofafluid actuated fastener driving device including the resilient pistonstop structure of this invention.

FIG. 2 is a cross sectional view of the device shown in FIG. 1 showingthe working piston at the end of its working stroke.

DESCRIPTION OF THE PREFERRED EMBODIMENT As just indicated, FIGS. 1 and 2illustrate a fastener driving too] including the resilient piston stopstructure of this invention. The tool shown in these Figures isdescribed in great detail in copending application Ser. No. 210,812filed Dec. 22, 1971 in the names of Robert G. Rothfuss and Carl T.Becht. The tool does not per se form a part of this invention. Hence, itwill be described only very briefly below.

The tool body includes a head portion indicated generally at 10, arearwardly extending'handle portion indicated generally at 12, a nosepiece or guide body indicated generally at 14, a magazine structureindicated generally at 16, and a manually actuated trigger 18.

Disposedwithin the head portion 10 is the main or the working cylindersleeve indicated generally at 20. Slidably disposed within the cylindersleeve is the piston indicated generally at 22. By comparing FIGS. 1 and2, it will be seen that the piston is movable from an initial positionadjacent the top of the cylinder sleeve (FIG. 1) to a down positionadjacent the other end of the cylinder sleeve (FIG. 2).-

The fastener driver indicated at 24 is carried by the piston, as will beexplained in more detail hereinafter.

In operation, the tool will be connected in a conventional manner to asuitable source of fluid under pressure, in this case, compressed air.The magazine 16 will be loaded with a supply of fasteners in strip formwhich are urged by the magazine toward an internal passage or drivetrack 14a in the nose piece of the tool. As seen in FIG. 1, in theinitial position the lowermost end of the driver 24 is disposed slightlyabove the head of the fastener positioned in the drive track 1421.

Upon actuation of the manual trigger l8, and as a consequence of valvingstructure which does not form a part of this invention, air underpressure will be admitted via the slots 26 into the cylinder sleeveabove the piston 22. This air under pressure serves to rapidly drive thepiston 22 and driver 24 downwardly in a working stroke to the positionshown in FIG. 2. At this time, a portion of the air under pressure inthe working cylinder is bypassed or conducted into a return reservoirfor ultimate use in returning the piston.

In normal operation, release of the manual trigger 18 by the operator iseffective to prevent further air under pressure from entering the slots26, and to vent the upper portion of the cylinder sleeve 20 toatmosphere. At this time, air under pressure in the return reservoir iseffective to act on the underside of the piston 22 and force it upwardlyto the original position shown in FIG. 1.

Plenum type return systems in connection with fastener driving tools areshown in detail in US. Pat. No. 26,262 in the name of A. G. .luilfs,dated Sept. 5, 1967 and entitled Portable Stapler With Pneumatic Driveand Return". The specific valving structure and return operation of thedevice shown in this application are explained in detail in copendingapplication Ser. No. 210,812 referred to earlier.

In the embodiment illustrated, the piston indicated generally at 22includes the relatively light weight shell 28. The shell 28 may be madeof aluminum or any other suitable material. The shell is provided on itsouter periphery with a groove 28a which carries the O- ring 30 in orderto maintain a sealing relationship with the cylinder sleeve 20 duringboth the drive and return strokes.

The underside of the piston shell 28 is provided with the counterbores32 and 34 which receive the unitary driver assembly to be describedhereinafter. The piston shell 28 isalso provided with the downwardlyextending, annular skirt portion 36 which is undercut so as to providean annular bead 38.

The unitary driver assembly briefly mentioned earlier comprises thedriver 24, the central hub 40, and the hub mounting plate 42. As shownin the drawings, these are preferably three separate components whichare secured together in any satisfactory manner so as to provide aunitary assembly. It will be apparent that the hub 40 and mounting plate42 respectively are received in the counterbores 32 and 34 in the pistonshell.

The resilient piston stop member 44 is provided with a central aperture45 through which the driver 24 extends and with the annular groove 46 sothat it will snap into place within the depending skirt 36 with the head38 engaged in the groove 46. In this manner, the unitary driver assemblymay be resiliently and detachably secured to the piston shell 28.

It will be observed that the upper surface of the member 44 is providedwith the circular, semi-cylindrical relieved area 48. This is necessaryin order to preventundue shearing acting caused by relative movementbetween the mounting plate 42 and the shell 28 during stopping.

Adjacent the bottom of the working cylinder, a second resilient pistonstop member 50 is provided. The resilient member 50 is exactly identicalto the member 44 but it is disposed upside down. That is, it is providedwith a central aperture 51, an annular groove 52, and a circular,semi-cylindrical relieved area 54. When fitted into an appropriatecavity in the bottom of the tool casting or cylinder sleeve as the casemay be, an annular bead will be engaged in the groove 52.

-The effective life of a resilient piston stop is believed to bedetermined by three primary characteristics. These are the load applied(in other words, the force exerted by the piston), the stopping distance(the distance between the first contact of the moving member and thefinal position of the moving member), and the amount of working" theresilient member undergoes. The amount of working of the resilientmember is based largely on what may be called the shape factor. Theshape factor, for purposes of this application, may be defined as theratio of the loaded area of the member to the free area of the member.In the case of the embodiment illustrated, the ratio will be equal tothe area of the impact face to the unconfined side wall area of themember plus the area of the central aperture.

It is very important to the success of this invention that the resilientmembers 44 and 50 be substantially identical in size in order to dividethe force and derive full benefit from the utilization of two separateresilient members.

In terms of fastener driving tool design, it will be assumed that a toolis to be built having a given piston diameter, piston velocity, andtotal force or energy. If stopping distance can be increased, resilientpiston stop life can be increased by making a taller resilient member sothat the working on the member is lessened. However, in the case offastener driving devices, the

. stopping distance is also a fixed parameter. Under these described inthis application, the total ratio of loaded area to free area of theresilient members is effectively doubled, and greatly increased pistonstop life is possible.

It is believed that the foregoing constitutes a full and.

complete disclosure of this invention, and no limitations are intendedexcept insofar as specifically set forth in the claims which follow.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a fastener applying device having a cylinder, a pistonreciprocable in said cylinder a fastener driver, and means for movingsaid piston and fastener driver in a driving stroke to drive a fastenerinto a workpiece; an improved piston stop structure comprising:

first and second resilient members of substantially equal size, one ofsaid members being fixedly mounted at the end of said cylinder, theother of said members being carried adjacent the side of said pistonfacing said one member, each said resilient member having a centralaperture for the p'assage of said fastener driver, i

and the area of the impact face of each of said resilient members beingequal to the unconfined side wall area plus the area of the centralaperture of the respective resilient member.

2. The improved piston stop structure claimed in claim 1 including meansfor resiliently and releasably securing said other of said resilientmeans to said piston.

3. The improved piston stop structure claimed in claim 2 wherein saidmeans for resiliently and releasably securing said other of saidresilient members to said piston is effective to resiliently secure saidfastener driver to said piston.

4. The improved piston stop structure claimed in claim 2 including amounting plate secured to the upper end of said fastener driver, andwherein said fastener driver extends through said aperture in the otherof said resilient members with said mounting plate against the surfaceof said other of said resilient members, whereby said means for securingsaid other of said resilient members to said piston is effective toresiliently secure said fastener driver to said piston.

5. In a device having a cylinder, a piston slidable in said cylinder,and means for driving said piston at high velocity toward one end ofsaid cylinder; and improved piston stop structure comprising:

a. a first resilient member mounted at said one end of said cylinder;

b. a second resilient member carried by the side of said piston facingsaid one end of said cylinder, said first and second resilient membersbeing substantially equal in size,

and the area of the impact face of each of said resilient members beingequal to the unconfined side wall area plus the area of the centralaperture of the respective resilient member.

6. The improved piston stop structure claimed in claim 5 wherein theside of said piston facing said one end of said cylinder includes anannular depending skirt, a portion of said second resilient member beingsurrounded by said skirt.

member.

1. In a fastener applying device having a cylinder, a piston reciprocable in said cylinder a fastener driver, and means for moving said piston and fastener driver in a driving stroke to drive a fastener into a workpiece; an improved piston stop structure comprising: first and second resilient members of substantially equal size, one of said members being fixedly mounted at the end of said cylinder, the other of said members being carried adjacent the side of said piston facing said one member, each said resilient member having a central aperture for the passage of said fastener driver, and the area of the impact face of each of said resilient members being equal to the unconfined side wall area plus the area of the central aperture of the respective resilient member.
 2. The improved piston stop structure claimed in claim 1 including means for resiliently and releasably securing said other of said resilient means to said piston.
 3. The improved piston stop structure claimed in claim 2 wherein said means for resiliently and releasably securing said other of said resilient members to said piston is effective to resiliently secure said fastener driver to said piston.
 4. The improved piston stop structure claimed in claim 2 including a mounting plate secured to the upper end of said fastener driver, and wherein said fastener driver extends through said aperture in the other of said resilient members with said mounting plate against the surface of said other of said resilient members, whereby said means for securing said other of said resilient members to said piston is effective to resiliently secure said fastener driver to said piston.
 5. In a device having a cylinder, a piston slidable in said cylinder, and means for driving said piston at high velocity toward one end of said cylinder; and improved piston stop structure comprising: a. a first resilient member mounted at said one end of said cylinder; b. a second resilient member carried by the side of said piston facing said one end of said cylinder, said first and second resilient members being substantially equal in size, and the area of the impact face of each of said resilient members being equal to the unconfined side wall area plus tHe area of the central aperture of the respective resilient member.
 6. The improved piston stop structure claimed in claim 5 wherein the side of said piston facing said one end of said cylinder includes an annular depending skirt, a portion of said second resilient member being surrounded by said skirt.
 7. The improved piston stop structure claimed in claim 6 wherein said skirt is undercut to provide an annular bead adjacent the free edge thereof, and wherein said second resilient member includes an annular groove engageable by said bead to resiliently secure said second resilient member to said piston.
 8. The improved piston stop structure claimed in claim 6 including annular mounting means for said second resilient member, said mounting means confining only a portion of the side wall of said second resilient member. 